Speaker
Description
We have been studied the no-insulation (NI) technique and co-winding method with various metallic tapes. The improved thermal stability of NI test coils by bypassing the transport current into the transverse direction was experimentally confirmed and reported. However, there are the problems of the transient stability and the reduction of critical current of NI HTS coils due to the thermal and mechanical stress according to electromagnetic force and cooling process. In addition, in NI HTS coils, we could not expect an effect of NI winding technique when a normal transition occurs at the outermost part of the coils. Therefore, in this study, we propose to install the metallic protection rings composed of two or more rings with different electrical and mechanical properties on the outermost turn of NI coils to improve the thermal, mechanical and electrical stabilities. This protection rings are mechanically and electrically connected to NI coils in parallel. The current bypassing characteristics in the transverse direction and normal zone propagation property in NI test coil with/without copper protection ring was investigated experimentally. The current bypassing from the outermost part of NI test coil to the copper protection ring was observed and the local temperature rising at outer part of test coil due to thermal disturbance was suppressed. The detail experimental results by copper protection ring will be presented.
